2 package # hide the package from PAUSE
10 our $VERSION = '0.02';
12 use Scalar::Util 'refaddr';
14 use base 'Class::MOP::Class';
16 sub construct_instance {
17 my ($class, %params) = @_;
18 # create a scalar ref to use as
19 # the inside-out instance
20 my $instance = \(my $var);
21 foreach my $attr (map { $_->{attribute} } $class->compute_all_applicable_attributes()) {
22 # if the attr has an init_arg, use that, otherwise,
23 # use the attributes name itself as the init_arg
24 my $init_arg = $attr->has_init_arg() ? $attr->init_arg() : $attr->name;
25 # try to fetch the init arg from the %params ...
27 $val = $params{$init_arg} if exists $params{$init_arg};
28 # if nothing was in the %params, we can use the
29 # attribute's default value (if it has one)
30 $val ||= $attr->default($instance) if $attr->has_default();
31 # now add this to the instance structure
32 $class->get_package_variable('%' . $attr->name)->{ refaddr($instance) } = $val;
37 package # hide the package from PAUSE
38 InsideOutClass::Attribute;
43 use Class::MOP 'meta';
45 our $VERSION = '0.03';
47 use Scalar::Util 'refaddr';
49 use base 'Class::MOP::Attribute';
51 sub generate_accessor_method {
52 my ($self, $attr_name) = @_;
53 $attr_name = ($self->associated_class->name . '::' . $attr_name);
55 $' . $attr_name . '{ refaddr($_[0]) } = $_[1] if scalar(@_) == 2;
56 $' . $attr_name . '{ refaddr($_[0]) };
60 sub generate_reader_method {
61 my ($self, $attr_name) = @_;
63 $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) };
67 sub generate_writer_method {
68 my ($self, $attr_name) = @_;
70 $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) } = $_[1];
74 sub generate_predicate_method {
75 my ($self, $attr_name) = @_;
77 defined($' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) }) ? 1 : 0;
81 ## &remove_attribute is left as an exercise for the reader :)
91 InsideOutClass - A set of example metaclasses which implement the Inside-Out technique
98 InsideOutClass->initialize($_[0] => (
99 # tell our metaclass to use the
100 # InsideOut attribute metclass
101 # to construct all it's attributes
102 ':attribute_metaclass' => 'InsideOutClass::Attribute'
106 __PACKAGE__->meta->add_attribute('foo' => (
113 bless $class->meta->construct_instance(@_) => $class;
116 # now you can just use the class as normal
120 This is a set of example metaclasses which implement the Inside-Out
121 class technique. What follows is a brief explaination of the code
122 found in this module.
124 First step is to subclass B<Class::MOP::Class> and override the
125 C<construct_instance> method. The default C<construct_instance>
126 will create a HASH reference using the parameters and attribute
127 default values. Since inside-out objects don't use HASH refs, and
128 use package variables instead, we need to write code to handle
131 The next step is to create the subclass of B<Class::MOP::Attribute>
132 and override the method generation code. This requires overloading
133 C<generate_accessor_method>, C<generate_reader_method>,
134 C<generate_writer_method> and C<generate_predicate_method>. All
135 other aspects are taken care of with the existing B<Class::MOP::Attribute>
138 And that is pretty much all. Of course I am ignoring need for
139 inside-out objects to be C<DESTROY>-ed, and some other details as
140 well, but this is an example. A real implementation is left as an
141 exercise to the reader.
145 Stevan Little E<lt>stevan@iinteractive.comE<gt>
147 =head1 COPYRIGHT AND LICENSE
149 Copyright 2006 by Infinity Interactive, Inc.
151 L<http://www.iinteractive.com>
153 This library is free software; you can redistribute it and/or modify
154 it under the same terms as Perl itself.